The present invention relates to a method for the preparation of multiple glucosyl, branched-cyclodextrins.
Preparation of branched cyclodextrins, and utilization and development thereof have been in rapid progress due to their excellent physical properties such as high solubility. To date, there have been known methods for preparing single branched-cyclodextrins having one branched-dextrin such as .alpha.-1,4 glucane and panose attached to their cyclodextrin rings, and multiple branched-cyclodextrins having two branches of malto-oligosaccharides, such as glucose, maltose and maltotriose, attached to their cyclodextrin rings, for instance, diglucosyl-cyclodextrin having two glucoses attached to the same cyclodextrin ring, dimaltosyl-cyclodextrin having two maltoses attached to the same cyclodextrin ring and glucosyl- or maltosylcyclodextrin having glucose or maltose branches attached to the same cyclodextrin ring.
These cyclodextrins are prepared by allowing a cyclodextrin-synthesizing enzyme to act upon branched-dextrins or permitting a mixture of an .alpha.-1,4 glucan such as maltose or maltotriose or a branched-dextrin such as panose with a cyclodextrin to act upon a debranching enzyme. There is also a method for preparing branched-cyclodextrins by allowing a mixture of malto-oligosyl fluoride or glucosyl fluoride with a cyclodextrin to act upon a debranching enzyme.
Single-branched cyclodextrins having one branch are much higher in solubility than the original cyclodextrins, and can be used in wider applications. However, since such single-branched cyclodextrins having one branch, e.g., single-branched .beta.-cyclodextrin are affected by amylases of Aspergillus oryzae (Taka-amylase), there has been an increasing demand for cyclodextrins highly resistant to such enzymes and their efficient preparation.
In particular, there is now a strong demand for multiple glucosyl branched-cyclodextrins, since they are hardly affected by amylases and excel in solubility. However, the preparation of multiple glucosyl branched-cyclodextrins so far considered merely involves the conversion of branch portions of conventionally produced multiple maltosyl branched-cyclodextrins to glucosyl groups by cutting with glucoamylase. In addition, the yields of multiple maltosyl cyclodextrins in conventional methods are low and barely 22.3% at most. Thus, not until now has any efficient method for preparing multiple glucosyl branched-cyclodextrins been developed.
Heretofore, there have been known methods for producing from maltose, maltotriose, panose and cyclodextrins maltosylcy-cyclodextrins, maltotriosylcyclodextrins, panosyl-cyclodextrins and dimaltosylcyclodextrins with the use of reverse synthesis reactions of debranching enzymes such as pullulanase and, on the basis of such findings, the preparation of single and multiple branched-cyclodextrins has been established. Further, it has been known that multiple branched-cyclodextrins such as glucosyl-cyclodextrin maltosylcyclodextrin are formed from malto-oligosaccharides and glucosyl-cyclodextrins by reverse synthesis reactions of debranching enzymes. Still further, it has been known that branch portions bonded to such cyclodextrins can be cut into glucosyl groups under the action of glucoamylase.